Bug infestation of backyard bush - Ask Extension
Hello and thank you for your help. We have four large bushes that are a type of landscaping holly. Every summer, the bushes become infected with som...
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Bug infestation of backyard bush #875804
Asked July 03, 2024, 1:07 PM EDT
Hello and thank you for your help. We have four large bushes that are a type of landscaping holly. Every summer, the bushes become infected with some sort of insect and the leaves have significant die back. The affected area of the bush gets larger every year. We cannot find an insect on the bush, but there does appear to be some sort of webbing on the bush. We would like to know how to get rid of whatever has infected the bush and to help the bush recover. We would prefer to use an organic or less harsh form of pesticide. Any advice would be greatly appreciated. Thank you in advance!
Montgomery County Maryland
Expert Response
We do not see any indications of an insect presence or cause of damage. If you see insects and they aren't in these two photos, feel free to share more images so we can ID them. The webbing in the close-up is from spiders (not harmful), and the dieback is either due to environmental stress and/or infection from a fungus.
We can't determine from the symptoms alone which fungus might be responsible, but several can affect hollies, notably Web Blight (Rhizoctonia), and small twigs in addition to leaves can be killed by that kind of infection. It can be worse on hollies that are heavily pruned, as the dense growth that trimming promotes reduces air circulation through the foliage, allowing leaves to remain wet for longer after rain, dew, or irrigation, which are conditions that make it easier for spores to infect them. These hollies appear to have been regularly or heavily pruned, so that might be a contributing factor.
Since so many of the branch tips on the sides have died, we don't think it will leaf back out and fill-in with regrowth well, even if given a couple years to do so. Fungicide use is not recommended, in part because it cannot cure existing disease. You may want to either replace the plants or prune them back drastically, in order to rejuvenate the growth with new branching that can remain looser and not as dense. Granted, it will take the plants a few years to regain this size if you do prune, as you'd be removing most of the branches down to within a foot or so of the ground, most likely. A "renewal"-pruned plant like this would probably rebound faster than a new plant, given that the old plant already has an extensive root system to draw upon while the new one needs to get established, but either option could work.
If you prefer to keep the hollies as-is instead, the only recourse for now is to just trim out all dead branch tips (anything with no living leaves and darkened or shriveled twigs instead of live green-barked twigs). No pesticide or fertilizer is recommended or would offer much benefit. Keep an eye on its watering needs as this drought continues, and give them time to regrow if they are able. Most shrubs and evergreens do not produce new foliage this late into the growing season, having done so in spring and early summer, so it's not necessarily concerning if little new growth manifests in the next few months in the areas with sparse foliage left. It would be more expected at this point that they do the bulk of their recovery starting next spring.
Miri
We can't determine from the symptoms alone which fungus might be responsible, but several can affect hollies, notably Web Blight (Rhizoctonia), and small twigs in addition to leaves can be killed by that kind of infection. It can be worse on hollies that are heavily pruned, as the dense growth that trimming promotes reduces air circulation through the foliage, allowing leaves to remain wet for longer after rain, dew, or irrigation, which are conditions that make it easier for spores to infect them. These hollies appear to have been regularly or heavily pruned, so that might be a contributing factor.
Since so many of the branch tips on the sides have died, we don't think it will leaf back out and fill-in with regrowth well, even if given a couple years to do so. Fungicide use is not recommended, in part because it cannot cure existing disease. You may want to either replace the plants or prune them back drastically, in order to rejuvenate the growth with new branching that can remain looser and not as dense. Granted, it will take the plants a few years to regain this size if you do prune, as you'd be removing most of the branches down to within a foot or so of the ground, most likely. A "renewal"-pruned plant like this would probably rebound faster than a new plant, given that the old plant already has an extensive root system to draw upon while the new one needs to get established, but either option could work.
If you prefer to keep the hollies as-is instead, the only recourse for now is to just trim out all dead branch tips (anything with no living leaves and darkened or shriveled twigs instead of live green-barked twigs). No pesticide or fertilizer is recommended or would offer much benefit. Keep an eye on its watering needs as this drought continues, and give them time to regrow if they are able. Most shrubs and evergreens do not produce new foliage this late into the growing season, having done so in spring and early summer, so it's not necessarily concerning if little new growth manifests in the next few months in the areas with sparse foliage left. It would be more expected at this point that they do the bulk of their recovery starting next spring.
Miri
Hi Miri,
Thank you very much for your quick reply. We appreciate the benefit of your knowledge and your advice and suggestions. The plants leaf out well every spring and the dieback has generally occurred on new growth. There are black patches on leaf stems, which may be indicative of the fungal infection you suspect. We have not pruned them extensively other than to trim the top and a little bit of the sides. They have grown a lot in the 8 years we have been in our home (they were planted here when we bought the property). We will try opening them up a little with selective pruning to get some airflow inside the bush. We would like to keep them! Thanks again for your help. We are grateful!
Kind regards,
Erwin and Andree
Hello Erwin and Andree,
You're welcome, and thank you for the additional information. It sounds like the culprit may be fungal, though it would be hard to confirm. Since use of a fungicide is probably not practical (or may be ineffective to completely prevent future outbreaks, at least), all you can do for now is to just prune out the existing dieback and, as you noted, thin-out some crowded/dense branching if it's needed afterwards. Fortunately, it looks/sounds like the plants are tolerating the recurring damage well, at least.
Miri
You're welcome, and thank you for the additional information. It sounds like the culprit may be fungal, though it would be hard to confirm. Since use of a fungicide is probably not practical (or may be ineffective to completely prevent future outbreaks, at least), all you can do for now is to just prune out the existing dieback and, as you noted, thin-out some crowded/dense branching if it's needed afterwards. Fortunately, it looks/sounds like the plants are tolerating the recurring damage well, at least.
Miri
